Liquid formulations of amorphous solid and viscous liquid copolyesters, which undergo precipitation or hydrogel formations in aqueous media, respectively, have been described in the prior art as carriers for the controlled release of bioactive agents. These entailed (a) solutions of essentially amorphous lactide/glycolide copolymers in liquid cyclic compounds, such as N-methyl pyrrolidone (U.S. Pat. No. 4,938,763); and (2) viscous liquids of polyether-esters with or without the incorporation of lower viscosity liquid diluents comprising lower molecular weight polyether-ester (U.S. Pat. Nos. 5,612,052 and 5,714,159). However, the solid polyester-based composition of U.S. Pat. No. 4,938,763 required the use of a cyclic tissue-irritating solvent and the low molecular weight of the polymers did not support the formation of resilient, adhering films or mechanically compatible luminal liners, that are defined as a continuous internal cover for biological conduits. Meanwhile, the hydrogel-forming compositions of U.S. Pat. Nos. 5,612,052 and 5,714,159 were not designed to a yield resilient, tissue-adhering, mechanically compatible luminal liner but rather gel-like materials. This provided an incentive to pursue the study, subject of the present invention, which is directed to the use of special solutions of crystalline, high molecular weight copolyesters mixed with non-reactive liquid polymers as carriers of bioactive agents, which, upon application onto the luminal surface of biological conduits, transform in the presence of water (hydroform) into a tissue-adhering, cohesive, resilient internal cover or liner that is capable of the controlled release of its bioactive payload as required for treating the application sites. Shortly after the release of the bioactive agents, the liner degrades to compliant microlamella.